1. Field of the Invention
The present invention relates to the field of photography and, more specifically, to a photographic apparatus having structure for influencing the thickness distribution of a processing fluid spread across preselected portions of an integral negative-positive self-processable type film unit.
2. Description of the Prior Art
An important step in the processing of a self-processable film unit is to spread a processing fluid between a predetermined pair of adjacent layers of the film unit, subsequent to its exposure, in order to initiate a diffusion transfer process which develops the photoexposed image. In order to produce a quality final image, the thickness of the fluid must be distributed over the entire photoexposed area of the film unit in a substantially uniform manner.
The present invention relates to controlling the distribution of a processing fluid within an integral negative-positive self-processable type film unit, representative examples of which are disclosed in U.S. Pat. No. 3,415,644 and U.S. Pat. No. 3,594,165.
Basically, these integral film units are multilayer structures having a rupturable container, holding a processing fluid at a leading end thereof and a trap for collecting excess fluid at the trailing end. The multilayer structure includes a pair of outer support sheets, at least one being transparent, and a plurality of layers including photosensitive and image receiving layers sandwiched between the outer support sheets which are bound together along lateral edges thereof.
Subsequent to exposure of the photosensitive layer or layers through the outer transparent sheet, the film unit is advanced, leading end first, between a pair of pressure applying members for applying a compressive pressure progressively along the length of the film unit to rupture the container discharging the fluid between a predetermined pair of adjacent layers, and then to distribute the fluid.
Because the layers are bound together along the lateral edges thereof, there is more resistance to fluid flow adjacent these edges than in the center portion of the film unit. Consequently, the discharged mass of fluid tends to advance rearwardly along a tongue-shaped wavefronts with a greater concentration of fluid in the center than out at the lateral edges.
In order to compensate for the initial uneven distribution of fluid, it has been found to be advantageous to selectively apply a second compressive pressure to the central portion of the film unit in the path of the rearwardly advancing wavefront. This second compressive pressure has a secondary thinning effect at the center of the film unit thereby making more fluid available for use elsewhere. It is reasoned that this pressure may force part of the fluid away from the center toward the lateral edges.
U.S. Pat. No. 3,779,770 disclosed a film container having integrally formed distribution control surfaces or projections thereon for selectively applying the second compressive pressure to the film unit as it is advanced through a film withdrawal slot in the container to the pressure applying members. Also, reference may be had to U.S. Pat. No. 3,820,137 which discloses a self-developing camera having structure for engaging and deflecting a thin wall portion of the film container having the distribution members formed therewith for positively urging the control members into engagement with the center portion of a film unit being advanced through the film withdrawal slot.
The integral self-processable film units generally have an inherent stiffness and as a film unit progressively advances from the exit side of the pressure-applying members, in cantilever fashion, it tends to follow a natural and substantially planar path of travel which is defined by the inherent stiffness. It has been discovered that deflecting the film unit from the natural path of travel by inducing a gentle and large radius bend in it on the exit side of the pressure-applying members beneficially influences the uniformity of the thickness distribution of fluid within the film unit.
While it is well established that the uniformity of fluid thickness distribution can be influenced by bending it immediately after it has emerged from the pressure-applying members, the mechanisms which produce this effect are not well defined at the present time and depend, in general, on complex factors related to hardware-film interactions.
A self-developing camera having structure for inducing a bend in the film unit as it emerges from the pressure-applying members is disclosed in U.S. Pat. No. 3,810,211 issued to R. R. Wareham on May 7, 1974. The camera is of the compact, folding, single lens reflex type and includes a housing section which extends forwardly of a pair of pressure-applying members. A combination film bending or deflecting plate and light shielding member is mounted near the forward end of the housing section adjacent a film exit slot therein that is offset with respect to the natural or normal emerging path of travel of the film unit. The plate is mounted for movement between a folded position and an extended position wherein it is disposed in the emerging path of travel to intercept the emerging film unit, bending it to induce a curvature in it and guiding it to the film exit slot. The disclosed housing section is characterized by its conventional construction using a plurality of piece parts that must be sequentially assembled and adjusted to define the film exit slot and mount the deflecting plate in predetermined relationship with respect to the pressure applying members and exit slot.
Camera structure having a similar purpose is disclosed in copending U.S. application Ser. No. 554,780 filed Mar. 3, 1975, in the name of A. S. Ivester. Here a self-developing camera is disclosed having an integrally molded plastic housing section that includes an offset exit slot and a camming member for deflecting a film unit towards the exit slot, as it emerges from a pair of pressure applying members, to influence the distribution of a fluid processing composition being spread within the film unit. However, even though the foregoing disclosures teach how to thin out the thickness of the processing fluid in the central portions of the film unit, using either pre-roller or post-roller structure for applying a secondary pressure, the control of the thickness of the processing fluid along the lateral edges of these integral type film units is an ever present concern. For example, incomplete corner coverage of the picture area at the trailing end of the film unit is a particularly troublesome problem especially when the camera is being used at depressed temperatures where the viscosity of the processing fluid increases. This makes the fluid even more prone to adhere to the lateral margins thereby depleting its supply in this area before reaching the trailing end corners. It is therefore desirable not only to have the capability of thinning out the fluid thickness near the central portion of the film unit by causing it to migrate laterally but also to more effectively control its thickness once the laterally displaced fluid migrates toward the lateral margins of the film unit.
Consequently, the present invention is directed toward providing structure for controlling the fluid thickness in regions adjacent the lateral margins of the film unit.